Low Voltage Transmission Circuit

TECHNICAL DATA TELEPHONE SPEECH NETWORK WITH DIALER INT`ERFACE FEATURES - Low DC line voltage; operates down to 1.6V (excluding polarity guard) - Voltage regulator with adjustable static resistance - Provides a supply for external circuits - Symmetrical high-impedance inputs (64 kΩ) for dynamic, magnetic or piezo-electric microphones - Asymmetrical high-impedance input (32 kΩ) for electret microphones - DTMF signal input with confidence tone - Mute ILA1062/1062A PIN CONNECTION LN 1 16 15 SLPE AGC REG GAS1 2 GAS2 OR GAR MICMIC+ STAB 3 4 5 6 7 8 14 input for pulse or DTMF dialing - ILA1062: active HIGH (MUTE) - ILA1062A: active LOW (MUTE) ILA1062 or BT1062A ILA1062A 13 12 VCC MUTE DTMF IR VEE 11 10 9 - Receiving amplifier for dynamic, magnetic or piezo-electric earpieces - Large gain setting range on microphone and earpiece amplifiers - Line loss compensation (line current dependent) for microphone and earpiece amplifiers - Gain control curve adaptable to exchange supply - DC line voltage adjustment facility DESCRIPTION www.DataSheet4U.com The ILA1062 and ILA1062A are integrated circuits that perform all speech and line interface functions required in fully electronic telephone sets. They perform electronic switching between dialing and speech. The ICs operates at line voltage down to 1.6 V DC (with reduced performance) to facilitate the use of more telephone sets connected in parallel. All statements and values refer to all versions unless otherwise specified. The ILA1062 (ILA1062A) is packaged in a standard 16-pin plastic DIP and special plastic DIP with internal heatsink is also available. QUICK REFERENCE DATA Characteristic Line Voltage Operating Line Current Normal Operation with Reduced Performance Internal Supply Current Supply Voltage for Peripherals I CC VCC VCC = 2.8V Iline= 15mA Ip= 1.2mA Ip= 0mA 2.2 2.2 Symbol VLN I line 11 1 0.9 2.7 3.4 Test Condition Iline = 15mA Min 3.55 Typ 4.0 2.0 140 11 1.35 Max 4.25 Unit V Vdc mA mA mA V Voltage Gain microphone amplifier receiving amplifier Line loss compensation Gain Control Exchange Supply Voltage Exchange Feeding bridge Resistance GV 44 20 ΔGV Vexch Rexch 36 0.4 52 31 dB dB 5.8 60 1 dB V kΩ ILA1062/1062A BLOCK DIAGRAM VCC 13 10 - LN 1 5 IR GAR BT1062A ILA1062A + 4 QR MIC+ MIC- 7 6 + 2 GAS1 + DTMF (1) 11 www.DataSheet4U.com + 3 GAS2 dB - MUTE 12 SUPPLY AND REFERENCE CONTROL CURRENT LOW VOLTAGE CIRCUIT CURRENT REFERENCE 9 VEE 14 REG 15 AGC 8 STAB 16 SLPE (1) Pin 12 is active HIGH (MUTE) for ILA1062. Fig.1 Block diagram for ILA1062A ILA1062/1062A FUNCTIONAL DESCRIPTION Supplies VCC, LN, SLPE, REG and STAB Power for the IC and its peripheral circuits is usually obtained from the telephone line. The supply voltage is delivered from the line via a dropping resistor and regulated by the IC. The supply voltage VCC may also be used to supply external circuits e.g. dialing and control circuits. Decoupling of the supply voltage is performed by a capacitor between VCC and VEE . The internal voltage regulator is decoupled by a capacitor between REG and VEE. The DC current flowing into the set is determined by the exchange supply voltage Vexch , the feeding bridge resistance Rexch and the DC resistance of the telephone line Rline . The circuit has internal current stabilizer operating at a level determined by a 3.6 kΩ resistor connected between STAB and VEE (see Fig.6). When the line current (Iline) is more than 0.5mA greater than the sum of the IC supply current (ICC) and the current drawn by the peripheral circuitry connected to VCC (Ip) the excess current is shunted to VEE via LN. The regulated voltage on the line terminal (VLN) can be calculated as: VLN = Vref + ISLPE x R9 VLN = Vref + {(Iline - ICC - 0.5 x 10-3A) - Ip} x R9 At line currents below 9mA the internal reference voltage is automatically adjusted to a lower value (typically 1.6V at 1mA). This means that more sets can be operated in parallel with DC line voltage (excluding the polarity guard) down to an absolute minimum voltage of 1.6V. At line currents below 9mA the circuit has limited sending and receiving levels. The internal reference voltage can be adjusted by means of an external resistor (RVA). This resistor when connected between LN and REG will decrease the internal reference voltage and when connected between REG and SLPE will increase the internal reference voltage. Microphone inputs MIC+ and MIC- and gain pins GAS1 and GAS2 The circuit has symmetrical microphone inputs. Its input impedance is 64 kΩ (2 x 32kΩ) and its voltage gain is typically 52 dB (when R7 = 68k?; see Fig.6). Dynamic, magnetic, piezo-electric or electret (with built-in FET source followers) can be used. The gain of the microphone amplifier can be adjusted between 44 dB and 52 dB to suit the sensitivity of the transducer in use. The gain is proportional to the value of R7 which is connected between GAS1 and GAS2. Stability is ensured by two external capacitors, C6 connected between GAS1 and SLPE and C8 connected between GAS1 and VEE. The value of C6 is 100pF but this may be increased to obtain a first-order low-pass filter. The value of C8 is 10 times the value of www.DataSheet4U.com Vref is an internally generated temperature compensated reference C6. The cut-off frequency corresponds to the time constant R7 x C6. voltage of 3.7V and R9 is an external resistor connected between SLPE and VEE. Input MUTE (ILA1062A) In normal use the value of R9 would be 20?. Changing the value of R9 will also affect microphone gain, DTMF gain, gain control characteristics, sidetone level, maximum output swing on LN and the DC characteristics (especially at the lower voltages). When MUTE is LOW or open-circuit, the DTMF input is enable and the microphone and receiving amplifier inputs are inhibited. The reverse is true when MUTE is HIGH. MUTE switching causes only negligible clicking on the line and earpiece output. If the number of parallel sets in use causes a drop in line current to below 6 mA the DTMF amplifier becomes active independent to the DC level applied to the MUTE input. Fig.2 Equivalent impedance circuit Dual-tone multi-frequency input DTMF When the DTMF input is enable dialing tones may be sent on to the line. The voltage gain from DTMF to LN is typically 25.5 dB (when R7=68kΩ) and varies with R7 in the same way as the microphone gain. The signalling tones can be heard in the earpiece at a low level (confidence tone). Receiving amplifier IR, QR and GAR The receiving amplifier has one input (IR) and a non-inverting output (QR). The IR to QR gain is typically 31dB (when R4 = 100kΩ). It can be adjusted between 20 and 31dB to match the sensitivity of the transducer in use. The gain is set with the value of R4 which is connected between GAR and QR. The overall receive gain, between LN and QR, is calculated by subtracting the anti-sidetone network attenuation (32dB) from the amplifier gain. Two external capacitors, C4 and C7, ensure stability. C4 is normally 100pF and C7 is 10 times the value of C4. The value of C4 may be increased to obtain a firstorder low-pass filter. The cut-off frequency will depend on the time constant R4 x C4. Under normal conditions, when ISLPE >>ICC + 0.5mA + Ip, the static behaviour of the circuit is that of a 3.7V regulator diode with an internal resistance equal to that of R9. In the audio frequency range the dynamic impedance is largely determined by R1. Fig.2 show the equivalent impedance of the circuit. The output voltage of the receiving amplifier is specified for continuous-wave drive. The maximum output voltage will be higher under speech conditions where the peak to RMS ratio is higher. ILA1062/1062A Automatic gain control input AGC Automatic line loss compensation is achieved by connecting a resistor (R6) between AGC and VEE. The automatic gain control varies the gain of the microphone amplifier and the receiving amplifier in accordance with the DC line current. The control range is 5.8 dB which corresponds to a line length of 5 km for a 0.5mm diameter twisted-pair copper cable with a DC resistance of 176 ?/km and average attenuation of Z bal Z bal + R 8 = Z line (2) Z line+ R 1 If fixed values are chosen for R1, R2, R3 and R9, then condition (1) will always be fulfilled when To obtain optimum sidetone suppression, condition (2) has to be fulfilled which results in: R8 1.2dB/km. Resistor R6 should be chosen in accordance with the exchange supply voltage and its feeding bridge resistance. The ratio of start and stop currents of the AGC curve is independent of the value of R6. If no automatic line-loss compensation is required the AGC pin may be left opencircuit. The amplifiers, in this condition, will give their maximum specified gain. Zbal = x Zline = k x Zline R1 R8 Where k is scale factor; k = Sidetone suppression The anti-sidetone network, R1//Zline, R2, R3, R8, R9 and Zbal suppresses the transmitted signal in the earpiece. Maximum compensation is obtained when the following conditions are fulfilled: R9 x R2 = R1 x R 3 + ⎛ R 8 x Zbal ⎞ ⎜ ⎟ ⎝ R 8 + Zbal ⎠ (1) R1 The scale factor k, dependent on the value of R8, is chosen to meet the following criteria: - compatibility with a standard capacitor from the E6 or E12 range for Zbal - |Zbal//R8|<>R9 to avoid influencing the transmit gain. In practise Zline varies considerably with the line type and length. The value chosen for Zbal should therefore be for an average line thus giving optimum setting for short or long lines. ABSOLUTE MAXIMUM RATING Characteristic Positive Continuous Line Voltage Repetitive Line Voltage During Switch-on or Line Interruption Repetitive Peak Line Voltage for a 1ms Pulse per 5s Line Current Input Voltage on all other Pins Total Power Standard DIP Dissipation DIP with heatsink Operating Ambient Temperature Storage Temperature Junction Tempera